Scrapped the true Sith idea. Made the story five months after KotOR, not five years. Instead of meeting an apparition, you find the real Revan in the Sith tomb on Korriban, with Bastila.

Note that this would be late in the game, after you've found the Jedi Masters (have Vash on M4-78 instead). Anyway, Revan and Bastila tried to kill Darth Sion, but couldn't, because of his ability. They fled to the tomb and sealed themselves off, hoping to find a way to stop him.

The Exile tells them that he or she just fought Sion and couldn't kill him, either, and that Kreia said he's invincible on Korriban. Revan's like, "Who's Kreia?" Because Kreia is really Kae. Kreia shows up at the tomb and reunites with her old apprentice. They have a discussion and you find out who Kreia really is.

It is agreed that Sion and Nihilus are the biggest threat and even if Revan is set to dark side, Revan will not fight you because he or she knows you are a wound in the force and needs you to stop Nihilus.

You cannot fight Revan either. Kae will not allow you to harm her old friend and someone as useful as Revan is and threatens to kill herself and end you if you dare defy her.

Revan and Bastila join your party. Revan's face would be chosen by the player. The true Sith = Naga Sadow remnants idea could've been used in KotOR III, set 100 years after TSL, so Obsidian has a fresh start.